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Radiation-driven outflows play a crucial role in extracting mass and angular momentum from binary systems undergoing rapid mass transfer at super-Eddington rates. To study the mass transfer process from a massive donor star to a stellar-mass black hole (BH), we perform multidimensional radiation-hydrodynamical simulations that follow accretion flows from the first Lagrange point down to about a hundred times the Schwarzschild radius of the accreting BH. Our simulations reveal that rapid mass transfer occurring at over a thousand times the Eddington rate leads to significant mass-loss from the accretion disc via radiation-driven outflows. Consequently, the inflow rates at the innermost radius are regulated by two orders of magnitude smaller than the transfer rates. We find that convective motions within the accretion disc drive outward energy and momentum transport, enhancing the radiation pressure in the outskirts of the disc and ultimately generating large-scale outflows with sufficient energy to leave the binary. Furthermore, we observe strong anisotropy in the outflows, which occur preferentially toward both the closest and furthest points from the donor star. However, when averaged over all directions, the specific angular momentum of the outflows is nearly comparable to the value predicted in the isotropic emission case. Based on our simulation results, we propose a formula that quantifies the mass growth rates on BHs and the mass-loss rates from binaries due to radiation-driven outflows. This formula provides important implications for the binary evolution and the formation of merging binary BHs. [ABSTRACT FROM AUTHOR]

Supermassive stars with masses of M * ≃ 104–105 M⊙ are invoked as possible seeds of high-redshift supermassive black holes, but it remains under debate whether their protostar indeed acquires sufficient mass via gas accretion overcoming radiative feedback. We investigate protostellar growth in dynamically heated atomic cooling haloes (ACHs) found in recent cosmological simulations, performing three-dimensional radiation hydrodynamical simulations that consider stellar evolution under variable mass accretion. We find that one of the ACHs feeds the central protostar at rates exceeding a critical value, above which the star evolves in a cool bloating phase and hardly produces ionizing photons. Consequently, the stellar mass reaches M * ≳ 104 M⊙ unimpeded by radiative feedback. In the other ACH, where the mass supply rate is lower, the star evolves almost as a hot main-sequence star, emitting intense ionizing radiation. Then, the stellar mass growth is terminated around 500 M⊙ by photoevaporation of the circumstellar disc. Our simulations provide a formula of the final stellar mass determined either by stellar feedback or their lifetime as a function of the mass supply rate from the parent cloud. Combining the results with the statistical properties of star-forming clouds in high-redshift quasar progenitor haloes, we construct a top-heavy mass distribution of primordial stars over M * ≃ 100–105 M⊙, approximately following a power-law spectrum of |${\propto} M_\ast ^{-1.3}$|⁠. Their black hole remnants would be further fed via the dense debris disc, powering 'milliquasars' with a bolometric luminosity of L bol ≳ 1043 erg s−1. [ABSTRACT FROM AUTHOR]

Coalescence of intermediate-mass black holes (IMBHs) as a result of the migration toward galactic centres via dynamical friction may contribute to the formation of supermassive BHs. Here we reinvestigate the gaseous dynamical friction, which was claimed to be inefficient with radiative feedback from BHs in literature, by performing 3D radiation-hydrodynamics simulations that solve the flow structure in the vicinity of BHs. We consider a 104-M⊙ BH moving at the velocity v flow through the homogeneous medium with metallicity Z in the range of 0–0.1  Z ⊙ and density n ∞. We show that, if n ∞ ≲ 106 cm−3 and v flow ≲ 60 km s−1, the BH is accelerated forward because of the gravitational pull from a dense shell ahead of an ionized bubble around the BH, regardless of the value of Z. If n ∞ ≳ 106 cm−3, however, our simulation shows the opposite result. The ionized bubble and associating shell temporarily appear, but immediately go downstream with significant ram pressure of the flow. They eventually converge into a massive downstream wake, which gravitationally drags the BH backward. The BH decelerates over the time-scale of ∼0.01 Myr, much shorter than the dynamical time-scale in galactic discs. Our results suggest that IMBHs that encounter the dense clouds rapidly migrate toward galactic centres, where they possibly coalescence with others. [ABSTRACT FROM AUTHOR]

The super-Eddington accretion on to intermediate seed black holes (BHs) is a potential formation mode of supermassive black holes exceeding |$10^9\, \mathrm{ M}_\odot$| in the early universe. We here investigate how such rapid accretion may occur with finite amounts of heavy elements contained in the gas and dust. In our 1D radiation-hydrodynamics simulations, the radiative transfer is solved for both the direct ultraviolet lights emitted by an accretion disc and the diffuse infrared (IR) lights thermally emitted by dust grains. Our results show that the radiative force by the IR lights causes a strong feedback to regulate the mass accretion. The resulting mean accretion rate is lower with the higher metallicity, and there is the critical metallicity Z ∼ 10−2 Z⊙, above which the super-Eddington accretion is prevented by the radiation pressure of the IR lights. With this taken into account, we examine if the dusty super-Eddington accretion occurs in young galaxies using a simple model. We show that a sufficient number of galaxies at |$z$| ≳ 10 can be such potential sites if BHs accrete the cold dense gas with T ∼ 102 K, approximately the thermal equilibrium value at Z  = 10−2 Z⊙. We argue that the efficiency of the BH growth via the rapid accretion depends on the metallicity, and that the metallicity slightly lower than |$10^{-2}\, \mathrm{ Z}_\odot$| provides a chance for the most efficient growth. [ABSTRACT FROM AUTHOR]